1. Technical Field of the Invention
This invention relates generally to wireless communication systems and more particularly to radio frequency integrated circuits used within such communication systems.
2. Description of Related Art
Communication systems are known to support wireless and wire lined communications between wireless and/or wire lined communication devices. Such communication systems range from national and/or international cellular telephone systems to the Internet to point-to-point in-home wireless networks. Each type of communication system is constructed, and hence operates, in accordance with one or more communication standards. For instance, wireless communication systems may operate in accordance with one or more standards including, but not limited to, IEEE 802.11, Bluetooth, advanced mobile phone services (AMPS), digital AMPS, global system for mobile communications (GSM), code division multiple access (CDMA), local multi-point distribution systems (LMDS), multi-channel-multi-point distribution systems (MMDS), and/or variations thereof.
Depending on the type of wireless communication system, a wireless communication device, such as a cellular telephone, two-way radio, personal digital assistant (PDA), personal computer (PC), laptop computer, home entertainment equipment, et cetera communicates directly or indirectly with other wireless communication devices. For direct communications (also known as point-to-point communications), the participating wireless communication devices tune their receivers and transmitters to the same channel or channels (e.g., one of the plurality of radio frequency (RF) carriers of the wireless communication system) and communicate over that channel(s). For indirect wireless communications, each wireless communication device communicates directly with an associated base station (e.g., for cellular services) and/or an associated access point (e.g., for an in-home or in-building wireless network) via an assigned channel. To complete a communication connection between the wireless communication devices, the associated base stations and/or associated access points communicate with each other directly, via a system controller, via the public switch telephone network, via the Internet, and/or via some other wide area network.
For each wireless communication device to participate in wireless communications, it includes a built-in radio transceiver (i.e., receiver and transmitter) or is coupled to an associated radio transceiver (e.g., a station for in-home and/or in-building wireless communication networks, RF modem, etc.). As is known, the transmitter includes a data modulation stage, one or more intermediate frequency stages, and a power amplifier. The data modulation stage converts raw data into baseband signals in accordance with a particular wireless communication standard. The one or more intermediate frequency stages mix the baseband signals with one or more local oscillations to produce RF signals. The power amplifier amplifies the RF signals prior to transmission via an antenna.
As is also known, the receiver is coupled to the antenna and includes a low noise amplifier, one or more intermediate frequency stages, a filtering stage, and a data recovery stage. The low noise amplifier receives inbound RF signals via the antenna and amplifies then. The one or more intermediate frequency stages mix the amplified RF signals with one or more local oscillations to convert the amplified RF signal into baseband signals or intermediate frequency (IF) signals. The filtering stage filters the baseband signals or the IF signals to attenuate unwanted out of band signals to produce filtered signals. The data recovery stage recovers raw data from the filtered signals in accordance with the particular wireless communication standard.
Many of the components of the transmitter and receiver are adjustable to account for process variations as well as for differing power levels of received radio frequency (RF) signals and/or of varying power levels of transmitted RF signals. To adjust for differing levels of received RF signals, the radio receiver includes a received signal strength indication (RSSI) module. As is known, a received signal strength indication module measures the magnitude of a received signal (i.e., in voltage), which is converted into a corresponding power level (in dBm, which is the ratio of power in milliwatts). For radio frequency integrated circuits that include an integrated RSSI module, the RSSI module is subject to the same process variations as other components of the RFIC. As such, the measured RSSI value may be off by as much as 20%. In high performance applications, this error is unacceptable since, if the measured RSSI is skewed high due to process variations (e.g., RSSI value greater than corresponding desired power level), useable RF signals will be ignored. Conversely, when the process variations skews the measured RSSI low, the radio will believe it is receiving an RF signal when in fact it is not. This later case locks the radio in the receive mode.
Such RFICs are generally tested prior to incorporation into a wireless communication device such that RFICs that exhibit the above mentioned process variation errors are discarded. By discarding otherwise useable RFICs for process variations of the RSSI module, manufacturing costs increase, which causes a domino effect of increased costs for wireless communication equipment and services.
Therefore, a need exists for a method and apparatus for calibrating received signal strength indication within a radio frequency integrated circuit.